933.    FINZEL, T. G.  Pyrophoric Iron.  I.  Preparation and Properties.  Jour. Am. Chem. Soc., vol. 52, 1930, pp. 142-149; Chem. Abs., vol. 24, 1930, p. 1275.

      Pyrophoric Fe can best be prepared by the reduction of Fe₂O₃ in H₂ at 500° for 3 hr.  The Fe₂O₃ was precipitated from Fe (NO₃)₃ solutions of different concentrations to produce oxides of different degrees of dispersion, which, in turn, would influence the pyrophoric activity of the reduced Fe.  The pyrophoric Fe was inactivated by heating in H₂, N₂, or He.  Oxides of the highest degree of dispersion yield pyrophoric Fe most easily inactivated – the ease of inactivation depending upon the degree of dispersion.  The time factor of inactivation for the different gases varied in the order:  He>N₂>H₂.  Inactivation is accompanied by a decrease in total surface.  Samples were produced that displayed pyrophoric activity at –78° and in air that had been thoroughly dried.